This disclosure relates to components for a gas turbine engine, such as airfoils. More particularly, the disclosure relates airfoils that are electro discharge machined.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
Turbine vanes used in the turbine section are manufactured as either single vanes, vane doublets, or multiple vanes combining quantities of more than two vanes. Multiple combined vanes such as this may have cooling holes that are not in a location that provides gun barrel line of sight from the machine tool to the hole location. Without line of sight access one way to machine these cooling holes is to use complicated tooling and programming to gain access to the intended location on the external airfoil. The obstructed hole is machined externally.
Turbine airfoil cooling hole position is typically inspected at the external hole breakout to gain some level of confidence that the hole is breaking into the intended internal cavity. However on multiple combined vanes the feature location cannot be inspected since the hole cannot be viewed from the gun barrel axis of the hole. Since the location of the holes cannot be accurately measured from the external surface, there exists some risk that the hole may not be drilled into the intended cavity.
The two manufacturing methods typically utilized for the machining of cooling holes in turbine airfoils are electro discharge machining (EDM) and laser. Many turbine airfoils have a thermal barrier coating applied to the airfoil surfaces and sometimes this is done prior to the installation of cooling holes. The thermal barrier coating is non-conductive so this prevents the use of the EDM process when machining the cooling holes from the external part surface. In these instances the only option is laser hole drilling, which does not have as much dimensional control when compared to EDM and also is not capable of non-line of sight machining.